HTMLRewriter

addEventListener("fetch", event => {
  event.respondWith(handleRequest(event.request))
})

class ElementHandler {
  element(element) {
    console.log(`Incoming element: ${element.tagName}`);
    switch (element.tagName) {
      case 'script':
      case 'style':
      case 'iframe':
        element.remove();
      break;
    }
    switch (element.tagName) {
      case 'b':
      case 'strong':
      case 'i':
        element.tagName = 'span';
      break;
    }
    element.removeAttribute('style');
  }

  comments(comment) {
    comment.remove();
  }

  text(text) {
    console.log(`Incoming text: ${text.text}`)
    if (/^\s*$/.test(text.text)) {
      text.remove()
    }
  }
}

async function handleRequest(request) {
  const r = new Response(`
  <div class="test">
    <!-- comment -->
    Pipa
    <script src="a.js">alert('hello')</script>
    <b style="font-size: 20px">
      some more text
      <script src="a.js">alert('hello')</script>
      <style>p { font-size: 42px }</style>
    </b>
  </div>
  <b style="font-size: 20px">some more text</b>
  `)
  const h = new HTMLRewriter().on('div.test *', new ElementHandler())

  return h.transform(r);
}